Hi @CathrineB ,
Do you want to update images to Dynamics 365 Finance and Operations?
Could you tell me where do the images data come from?
1)If it is taken by camera control, the data will be save as binary.
You could use "camera name.Photo" to represent the captured pictures.
You could also save the captured pictures in a collection to use.
Collect(pic,{data:camera name.Photo})
2)If it comes from local by using Add Picture control, the images could be saved in collection as binary too.
You could also save the adding pictures in a collection to use.
Collect(pic,{data:UploadedImage1.Image})
What's more, if you want to the collection stored image binary data when you open the app, I'm afraid it's not supported.
You need to act action like "choose images" in add picture control or "take picture" in camera control, then the image data will be saved in powerapps.
Just opening the app is not enough.
After you save the images as binary, you could use flow to update data.
Here's a similar issue for your reference:
https://powerusers.microsoft.com/t5/Building-Power-Apps/Uploading-Image-to-Dynamics-365-through-PowerApps-Microsoft-Flow/td-p/182767
Best regards,